Idiopathic Scoliosis (IS) (e.g., Infantile Idiopathic Scoliosis, Juvenile Idiopathic Scoliosis or Adolescent Idiopathic Scoliosis (AIS)) is a spine deformity of unknown cause generally defined as a lateral curvature greater than 10 degrees accompanied by a vertebral rotation1. The condition affects 4% of the paediatric population and is most commonly diagnosed between the ages of 9 to 13 years2,3,4. The diagnosis is primarily of exclusion and is made only after ruling out other causes of spinal deformity such as vertebral malformation, neuromuscular or syndromic disorders. Traditionally, the trunkal asymmetry is revealed by Adams forward bending test and measured with scoliometer during physical examination5. The diagnosis can then be confirmed by radiographic observation of the curve and the angle measurement using the Cobb method6.
Once diagnosed, the primary concern for physicians in managing scoliotic children is whether the curve will progress. Indeed, the curve progression is often unpredictable and is more frequently observed among girls than in boys7. If untreated, the curve can progress dramatically, creating significant physical deformity and even cardiopulmonary problems. These manifestations become life threatening when the curve exceeds 70 degrees8,9. The current treatment options to prevent or stop curve progression include bracing and surgery. In general, bracing is recommended for curves between 25 and 40 degrees, while surgery is reserved for curve greater than 45 degrees or curves that are unresponsive to bracing.
Today in the United States there are approximately one million children between ages 10 and 16 with some degree of IS and about 100 000 children in Canada are diagnosed with IS. The total cost of diagnosis and monitoring of the scoliotic children by X-ray exposure is over $2.5 billion dollars annually in North America. Approximately, 10% of children diagnosed with idiopathic scoliosis have curve progression requiring corrective surgery10. About 29,000 scoliosis surgeries are done every year in North America, resulting in significant psychological and physical morbidity.
Currently, there is no approved method or test available to identify subjects at risk of developing IS or to predict which affected individuals will show a curve progression that will require surgery. Therefore, the application of current treatments, such as bracing or surgical correction, is delayed until a significant deformity is detected or until a significant progression is clearly demonstrated, resulting in a delayed, less than optimal treatment and often important psychological sequels (Scoliosis Research Society) Morbidity & Mortality Committee annual Report 1997). All diagnosed children are subjected to multiple radiographs over several years, usually until they reach skeletal maturity. It is estimated that the typical patients with scoliosis will have approximately 22 radiological examinations over a 3-year period11. Because of the potential risk of multiple radiographic examinations, the alternative approaches that could allow performing the prognosis of idiopathic scoliosis without exposing children to ionizing radiation are strongly desirable.
The major limitation in developing prognostic tests that could facilitate treatment choices for patients is the heterogeneous nature of IS. At the clinical level, the heterogeneity of IS is clearly illustrated by the variability of curve patterns, localisations and curve magnitude even in families with multiple affected members. In absence of reliable IS phenotypes, there is a need to understand better the molecular changes associated with disease onset and spinal deformity progression. Molecular definition of disease is rapidly replacing traditional pathology-based disease descriptions in part because of its utility in identifying the optimal treatment regimen for patients.
In this regard, the present inventors have previously discovered that scoliotic patients and subjects at risk of developing scoliosis are less responsive to Gi protein (inhibitory guanine nucleotide binding protein in G protein coupled receptors (GPCRs) also known as Gi alpha subunit) stimulation when compared with healthy control subjects. The presence of a general differential Gi-signaling dysfunction allowed to stratify/classify patients into three functional groups (FG1, FG2 and FG3) representing distinct biological endophenotypes. This impairment was detected in all cell types tested including bone-forming cells; muscle-forming cells and blood cells (e.g., PBMCs). Furthermore, because the response impairment is generalized and not specific to a particular receptor, any Gi-PCR agonist can be used to classify subjects.
A first classification method is based on the percentage of degree of reduction (inhibitory response) relative to control group. The classification ranges were fixed between about 10 and 40% (or below 40%) of reduction of response relative to control group for FG3, about 40 and 60% for FG2 and above about 60% (e.g., between about 60% and 90%) for FG1. The same the classification ranges can be expressed as the percentage of maximal response relative to the control (as opposed to the % of reduction of response relative to the control). In such a case, the ranges are fixed between about 10-40% for FG1, about 40 and 60% for FG2 and about 60-90% for FG3. Both classification ranges can be used interchangeably (See Moreau et al., 2004; Akoume et al., 2010; Azeddine et al., 2007; Letellier et al., 2008; WO2003/073102, WO2010/040234 to Moreau, which are incorporated herein by reference in their entirety).
More recently, the present inventors have modified this approach by demonstrating that the three functional groups can clearly be distinguished according to the profile of imbalance between response to Gi and Gs stimulation (i.e. Gi response minus Gs response or Gi/Gs-See PCT/CA2014/050562, which is incorporated herein by reference). It was found that the response to Gi stimulation predominated in FG3, while no substantial imbalance (or a very small imbalance) was observed in FG2. In contrast, FG1 exhibited predominance for response to Gs stimulation. In addition, evidence was provided to the effect that patients belonging to the FG2 endophenotype are more at risk of progressing to the point of needing surgery17.
The differences in Gi-mediated cellular response observed among the three endophenotypes is (at least partly) a consequence of differences observed at the level of Gi protein phosphorylation. When Giα proteins are phosphorylated they become inactive. The inventors have shown that the degree of serine phosphorylation of Giα proteins can alternatively be used to classify subjects into a specific functional groups. In FG1 subjects, all Giα proteins (Giα1-3) are phosphorylated and their level of serine phosphorylation is substantially higher than in control subjects. In FG2 Giα1 and Giα2 are phosphorylated, the level of Giα1 and Giα2 phosphorylation is higher than in control subjects and most Giα3 proteins are not phosphorylated and thus, remain functional. Finally, in FG3 subjects Giα2 and Giα3 are phosphorylated, their level of phosphorylation is higher than in control subjects and most Giα1 are not phosphorylated and thus remain functional18.
The assessment of an imbalance between Gi and Gs coupled receptor signaling (as opposed to the assessment of a Gi-coupled receptor signaling impairment), greatly simplifies the risk assessment and endophenotype (functional group) assessment by eliminating the need of a reference signal from a control subject. The establishment of a reference signal is often difficult and may sometimes constitute an obstacle because the control subject(s) from whom the reference signal is derived should preferably match with age, gender and medication, if any.
Although the methods of diagnosing subjects suffering from scoliosis or at risk of developing scoliosis described above provide significant advantages, certain subjects are more difficult to classify into a functional group (FG1, FG2 or FG3) because their response to Gi stimulation or degree of Gi/Gs imbalance approaches the cut-off values defined for the classification. Furthermore, determining the phosphorylation level/pattern of Giα proteins may be more difficult to implement in a clinical setting. Therefore there is a need for novel alternative or complementary methods for classifying subjects having diseases involving spinal deformities (e.g., scoliosis, such as IS) and for diagnosing a predisposition to scoliosis.
The present description refers to a number of documents, the content of which is herein incorporated by reference in their entirety.